This invention relates to a device for wiping the optical window in a turbidimeter or other similar optical instrument for examining a liquid sample. More particularly, the present invention relates to a method and device for easily and quickly wiping the inner surface of a sample cell in a turbidimeter or other similar optical instrument which has the sample cell provided therein as part of the path for a liquid sample at a position falling within the path of light extending from a light source to a measuring unit, so that the degree by which the beam of light emitted from said light source in the direction of the measuring unit is attenuated by suspended solid particles present in the liquid sample in motion through the sample cell is measured on the measuring unit and, based on the result of the measurement, the content of the suspended solid particles in the liquid sample is determined.
It is widely known that a turbidimeter designed to determine the amount of suspended solid particles contained in a given liquid sample in terms of turbidity, for example, makes use of an integrating sphere (an Ulbricht sphere) as means for measuring the amount of incident light and effects determination of the turbidity of the liquid sample by a procedure comprising the steps of projecting a collimated beam of light from a light source toward the integrating sphere, allowing the beam of light to pass into a sample cell so that during the passage of the beam of light through the sample cell, the part of the beam of light which impinges upon the suspended solid particles present in the liquid sample held inside the sample cell is diffused and the remaining part of the beam of light which escapes the impingement is allowed to advance straight through the sample cell, measuring the intensity of the diffused light and that of the undiffused light on separate light-receiving elements annexed to the integrating sphere and comparing the measured intensities. Needless to say, the means for measurement of the amount of incident light is not limited to the integrating sphere. For any measuring instrument of the type which is designed to accomplish the determination of the amount of suspended solid particles present in a liquid sample by causing a beam of light issuing from a light source to pass through a sample cell for thereby having the beam of light attenuated by suspended solid particles contained in the liquid sample and measuring the degree of the attenuation, however, when the inner surface of the sample cell which falls in the path for the beam of light happens to be smeared with a remnant of the suspended solid particles contained in the liquid sample passed through the sample cell in the previous test run, then the value of measurement obtained by the instrument is inclusive of a portion ascribable to the solid particles adhering to the cell surface in the path for the beam of light and, therefore, fails to represent exactly the amount of suspended solid particles contained in the liquid sample under test. The smear of the cell surface thus prevents the instrument from providing an accurate measurement, no matter whether the precision of the turbidity itself may be improved even to a point where the turbidity will be accurately measured to the finest degree.
For this reason, there have been proposed measures for cleaning the inner surface of the sample cell to remove adhering solid particles by means of ultrasonic waves or water jets. The proposed measures in their existing state, however, are not effective enough to provide thorough removal of the adhering solid particles. In the circumstances, there is still adopted a method whereby the instrument is disassembled to remove the sample cell therefrom and the inner surface of the sample cell is wiped manually. According to this manual method, the instrument must be disassembled to permit removal of the sample cell and reassembled after completion of the wiping work. Thus, the wiping work inevitably keeps the instrument out of service for a long time and entails much time and labor in the disassembling and reassembling works.